Infusion Pump System with Disposable Cartridge Having Pressure Venting and Pressure Feedback

1. A delivery mechanism of an infusion pump for dispensing fluid to a patient, the delivery mechanism comprising: a spool slidingly disposed in a bore of a delivery mechanism housing; and an o-ring seal disposed on the spool, the o-ring seal comprising: a gland for seating an o-ring including an outer circumferential groove extending circumferentially around a longitudinal axis of a cylindrical body of the spool, the circumferential groove including an angled first surface and an angled second surface opposite the angled first surface and an inner overflow channel disposed below the angled first and second surfaces and including a pair of sidewalls each extending downwardly from and at an angle to one of the angled first and second surfaces and a bottom; and an o-ring disposed in the gland with a first circumferential band of the o-ring resting on the first angled surface and a second circumferential band of the o-ring resting on the second angled surface above the overflow channel with the o-ring in a substantially uncompressed state.

2. The mechanism of claim 1 wherein the angled first and second surfaces form a total inclusive angle with each other of about 20 degrees to about 60 degrees.

3. The mechanism of claim 1 wherein an outer surface of the o-ring rests above a nominal outer surface of the cylindrical body and does not extend substantially into the overflow channel when the o-ring is in an uncompressed state.

4. The mechanism of claim 3 wherein a center of a cross section of the seal element of the o-ring is disposed below the nominal outer surface of the cylindrical body when the o-ring is in a substantially uncompressed state.

5. A delivery mechanism of an infusion pump for dispensing fluid to a patient, the delivery mechanism comprising: a spool slidingly disposed in a bore of a delivery mechanism housing; and an o-ring seal disposed on the spool, the o-ring seal comprising: a gland for seating an o-ring including an outer circumferential groove extending circumferentially around a longitudinal axis of a cylindrical body, the circumferential groove including a first circumferential surface and a second circumferential surface opposite the first circumferential surface, and an inner overflow channel portion having a bottom; and an o-ring disposed in the gland in an axially compressed state, the o-ring being axially compressed by the first and second circumferential surfaces and disposed above the overflow channel and not contacting the bottom of the overflow channel portion.

6. The mechanism of claim 5 wherein the first and second circumferential surfaces of the groove are straight-walled surfaces that form a total inclusive angle with each other of up to about 5 degrees.

7. The mechanism of claim 5 wherein an outer surface of the o-ring rests above a nominal outer surface of the cylindrical body.

8. The mechanism of claim 7 wherein a center of a cross section of the seal element of the o-ring is disposed below the nominal outer surface of the cylindrical body.

9. The mechanism of claim 5 wherein the O-ring has an axial compression of about 60 percent to about 85 percent.

10. The mechanism of claim 1 , wherein the o-ring does not contact the bottom of the overflow channel when in the substantially uncompressed state.